In a process of manufacturing electronic components or semiconductor products, forming thin films and etching in a vacuum apparatus are indispensable processes. In this case, it is a general practice to proceed with the process while keeping the internal pressure of the vacuum apparatus constant. As a pressure gauge for measuring the internal pressure of the vacuum apparatus in the process, a diaphragm-type pressure gauge is often used, which can perform accurate pressure measurement regardless of the type of gas.
FIG. 10 is a view showing an example of the structure of a conventional diaphragm-type pressure gauge (PTL 1). A diaphragm-type pressure gauge with such a single diaphragm structure has a pressure measurement range of two to four orders of magnitudes. This is because the amount of displacement of the diaphragm is very small on the low pressure range side, and a variation of the diaphragm is not proportional to a pressure on the high pressure range side. For this reason, when measuring a wider pressure range with such a diaphragm-type pressure gauge, it is necessary to perform pressure measurement by preparing a plurality of diaphragm-type pressure gauges having different measurement pressure ranges and individually measuring output voltages from the respective pressure gauges. The diaphragm-type pressure gauge disclosed in PTL 1 includes a correction electrode 10 located at a position out of the center of a diaphragm electrode 4 (diaphragm-type pressure detection element) so as to face it. The capacitance detected by a fixed electrode 5 is corrected by the capacitance detected by the correction electrode 10 to reduce the influence of an ambient temperature on pressure measurement. Even with the function of this correction electrode, however, output voltage fluctuations due to ambient temperature fluctuations are unavoidable. For this reason, the diaphragm-type pressure gauge includes a potentiometer or switch for modifying the fluctuation amount.
On the other hand, as shown in FIG. 11, a diaphragm-type pressure gauge having two diaphragm-type pressure detection elements (PTL 2) is known. The diaphragm-type pressure gauge disclosed in PTL 2 is manufactured by a micromachine technique using a semiconductor manufacturing process technique. A vacuum sensor chip having an insulating substrate 13 bonded to a silicon substrate 14 (constituted by an elastic structure 8 and a rigid structure 11) has a size of about several mm to several 10 mm and a thickness of about 1 mm. Combining the two diaphragm-type pressure detection elements having different measurement ranges makes it possible to measure a wider pressure range with a single diaphragm-type pressure gauge. A diaphragm-type pressure gauge like that disclosed in PTL 2 is generally configured to correct a capacitance influenced by ambient temperature fluctuations for each diaphragm-type pressure element by using the correction electrodes respectively provided for the two diaphragm-type pressure detection elements.